Throttle Plate Edging / Throttle Plate Screw Countersinking

Why would you do this:
You gain a few CFM (Cubic Feet per Minute) of flow through the throttle body. The throttle also feels more responsive.

What could go wrong:
I’ve have this mod for a while, but I was reluctant to post a DIY because my idle was unstable. Now my idle is rock solid, but I have no idea why? [IMG]i/expressions/face-icon-small-confused.gif[/IMG] The first time I did this modification I had a slightly elevated idle (by only 100rpm’s). I scratched up the throttle plate when I put it back into the throttle body, so I decided to redo everything. This time my idle was way way off. It was oscillating betwean 1,000rpm’s and 2,000rpm’s. It was hard to drive around in low gears at low rpm’s because the engine would sputter and shake as if it was being choked. I experimented with the IAC (Idle Air Control) valve and I couldn’t stabilize the idle. I finally just gave up and put the stock plastic cap back on. Then after driving around with it like that for a while my idle stabilized and the check engine light finally went off. Now I;ve driven around for more than 500 miles and everything seems like stock. Well, except for the better throttle response (attested to by my sister without me even saying anything).

Time needed:
Well, it’ll take you quite some time to get this done. I’de say that there’s enough work here for a whole weekend. That’s if you’ve never done this before. Then there’s even more work if something fouls up. Take your time to do it right and I’m sure that you’ll be happy with the results.

Required tools:
- Socket Wrench
- 10mm Socket
- Phillips Head Screwdriver
- Crescent Wrench
- Metal File
- Sand Paper (medium, fine, very fine)
- WD-40
- Window Cleaner (anything that cleans and dries fast)
- Countersinking Bit
- Electric Drill

First you’ll want plenty of light. Hehe, you can see my now famous lamp here. [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

Here’s a shot of the filter box. Notice how nice and shiny my engine bay is! It’s winter time too, but it’s just bean cleaned. Anyway, take off the three bolts holding the filter box down. They’re 10mm bolts and you’ll probably need an extention to reach the left-most (passenger side) one.

Take off the oxygen sensor connector. Just press on the little tab on the top and pull it off.

Pull back the little steel clamp holding the rubber hose going from the filter box to the valve cover.

Take a phillips head screwdriver and loosen the steel clamp that holds the filter box to the throttle body. Feel the back of the steel clamp with your other hand and notice where the screw threads through. Unscrew it almost all the way, but you don’t need to let the screw fall out. Just use your other hand to feel how far you’ve unscrewed it so far and stop before the end of the screw disappears into the threaded hole.

Remove the filter box by pulling up on it. You’ll want to pull up on it near the throttle body and then slide it out to the right (driver’s side) to disconnect it from the intake resonation chamber. You should jiggle it around a bit and pull up hard; you’ll get it eventually. You’ll be able to disconnect the tube leading from the filter box to the valve cover after you have the filter box disconnected from the throttle body.

This is what the underside of the filter box looks like. You can see the screw and the steel clamp as well as the rubber insert. The rubber insert may have been left on the throttle body when you pulled up on the filter box. Just take it off of the throttle body and put it back on the filter box. It’s coded to only go on one way; just take a good look at it and you’ll see what I mean.

Disconnect all of the sensors leading to the throttle body. The right-most (driver’s side) one also needs to be disconnected so that we have enough room for the screwdriver that we will use later on. You do not need to disconnect the battery. You can even have the radio playing in the car; just don’t turn the key past the first position.

Use a crescent wrench to remove the throttle cable and the A/C cable (if you have one) from their mounting locations near the throttle body. Then simply unthread the wires from the throttle body and take them out. Try to get a feel for how they will go back in. The little pegs at the ends are of different sizes, so you won’t get them mized up when you put them back in.

Separate the IAC valve from the throttle body. There are three phillips head screws holding it on to the throttle body. Make sure to do this step only when the car has cooled down enough for the coolant system to be depressurized. Some coolant will leak out when you separate the IAC valve from the throttle body, but only enough to fill a table spoon. Just wipe it up with something and don’t be tempted to taste it. Bleh…

Now disconnect the thing on the right side (driver’s side) of the throttle body. There are two phillips head screws holding it on. Now just use a 10mm socket to separate the throttle body from the intake manifold. There are three long bolts and one nut. The long stud helps you center the throttle body onto the intake manifold when you go to put everything back together. I love mechanic friendly designs! [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

Take out the throttle body. Remember to plug up the gaping hole leading in to the intake manifold with a clean rag so that no dirt gets in. Okay, I’m sick of saying throttle body; from now on throttle body = TB. Look inside and take out the two phillips head screws that hold the throttle plate to the throttle plate holder. Watch out not to let your hand slip; you don’t want to scratch anything up. The biggest thing you could mess up would be the edge of the throttle plate. Now mess with the part of the TB that tilts the throttle plate. Tilt it and take out the throttle plate by wiggling it out of it’s holder.

Now polish up the surface of the throttle plate. It’ll have some minor scratches on it and it might have some carbon buildup. I used three different grits of wet sanding sand paper; what this means is that you spray some water onto the surface and it acts as a sort of lubricant and coolant. I chose a very flat surface to work on so that I wouldn’t be sanding down the edges of the throttle plate. Use a mirror or a piece of glass if you have one. I can not stress this enough, DO NOT sand or file the egdes of the throttle plate!

Sorry for the quality of this picture, too little light I think. Anyway, the edges have been knife edged. The throttle plate is 1/16″ thick and I left a 1/32″ edge that comes into contact with the walls of the TB. I took off some material with a metal file from only those surfaces of the throttle plate whose angle with the TB walls decreases to parrallel when you open the throttle plate. Refer to the following diagram…

Now counterink the throttle plate holder on the back side of the throttle body. DO NOT countersink the side with the threads for the screws! Use light pressure and check on your progress from time to time. I have no idea what that metal is made out of, but my countersinking bit chewed through it easier than I would have thought. Now clean the TB with something like TB cleaner, but using anything that cleans and evaporates quickly is good for the job. Just don’t submerge the whole TB; doing so might damage the TPS (Throttle Position Sensor).

Here’s a little tip… Take some sand paper and sand the inside of the throttle plate holder. Just fold a piece of sand paper in half so that there’s sand paper on both sides. Then run it through the throttle plate holder while holding it open all the way. What you want to do it take out all of the rough edges (if there are any) around the area where the screws were holding the throttle plate to the throttle plate holder. You do this so that you don’t scratch up the newly polished throttle plate when you go to put it back in the TB. Notice the Loctite… We’ll use this when we put the throttle plate screws back in.

I doubt that you can buy the exact size of screw that you need. If you can, then more power to you. What I ended up doing was taking some stainless steel phillips head screws that I had laying around and filing then down to size. Mine were #8 with thread size 32, but I think the stock ones are metric. Didn’t matter much though, they threaded in okay and with the Loctite they’re not going anywhere.

Here’s what the finished TB looks like from the side of the filter box. Now, when you put in the throttle plate you’ll have to get it so that there’s equal space on one side and the other when it is closed. When you hold it up to the light you should see little to no light shine through the edges of the throttle plate. If you do, then you will have to adjust the little set screw that prevents the plate from closing all the way. Adjust it so that the throttle plate seals properly with the edges of the TB. Make sure that the throttle plate does not bind to the edges of the TB. After adjusting the little set screw you’ll have to adjust the TPS. More on that later…

Here’s what the finished TB looks like from the side of the intake manifold.

Here’s the payoff; a few more CFM of flow.

To adjust the TPS you’ll have to re-install everything back to this point. Then hook up a multimeter to the TPS by pushing in some pins into the TPS connector. Five volts goes in to the TPS. It should read .5 volts when closed and 4.5 volts when fully open (at WOT, Wide Open Throttle). It’s important to have it be as close as possible to .5 volts when closed, but not over. The factory sets this to just under .5 volts. You can adjust the TPS sensor with minute taps on it’s sides with a little piece of wood and a hammer. Watch the multimeter and give it a few taps. DO NOT tap too hard or you will break the plastic. Position the wooden block as close to the wall of the TB as you can so that you don’t break off the plastic on the sides of the TPS (which is rather thin). This method only works for minute adjustments. I’m talking .05 volts at the most. If you need anything more than that then I don’t know what to say… You messed something up. Go back and try to re-adjust the position of the throttle plate within the throttle plate holder. Technically you should never have to do this step if you do everything carefully.

Good luck!

Grey from civicforums

Both comments and pings are currently closed.

Comments are closed.